Nitric Oxide (NO) gas is a short-lived molecule normally found in a gaseous state both inside and outside the human body. NO is a signaling molecule known to have numerous regulatory, protective and therapeutic properties. Augmenting the body's natural generation of NO by either stimulating increased production of endogenous NO or introducing exogenously-produced NO into the body can improve the body's response to damage, pain, and invading organisms. However, it is difficult to deliver NO into living tissue and, in its gaseous state, NO does not penetrate through the dermis. To be clinically useful, NO must be present in the site of action in a sufficient quantity.
Prior techniques for delivering NO for therapeutic purposes include the administration of chemical compounds which release NO chemically into the body. Other methods employ NO pathway agonists and NO antagonists. Still other methods employ high pressure NO gas and sprays. Yet another method involves surrounding a body with sealed vacuum containers into which gaseous NO is introduced. Attempts have also been made to force pressurized nitric oxide through tissue and skin. For various reasons, these methods have yielded limited results. For example, gaseous NO is highly reactive, has low diffusion constant and has extremely short life-time in tissue media.
Another method that has failed to achieve clinical success involves the administration of molecular donors, which has been demonstrated to be problematic because the control of the release of the payload cannot be modulated, nor can the penetration/saturation of the donors be reliably modulated.
There are several solutions that target specific clinical outcomes involving NO. Sildenafil citrate (sold under the brand name VIAGRA), for example, interferes with the down regulation of NO in erectile dysfunction syndrome. Etanercept (sold under the brand name ENBRIL), for example, uses an anti-TNF alpha antibody to do what NO would do in inflammatory diseases of the joint. Most solutions involve affecting the NO pathways, due to the difficulty in stimulating production of NO directly at the site of action. Because of the lack of site specificity of these NO pathway pharmacologics, negative side effects can be serious.